Polycarbonate resin (hereinafter sometimes referred to as “PC”) has excellent heat resistance with its heat distortion temperature being high, further has excellent impact resistance and transparency, and is used in a wide range of fields such as exteriors, electronic and electric applications, optical disk substrates and automotive applications. However, in the case of using PC solely, there is a problem of poor molding processability because of its viscosity in the melt state higher than those of other thermoplastic resins, and it is strongly desired to improve molding processability (flowability) as molded products get thinner and larger. Moreover, PC also has a problem of poor chemical resistance, and there is a limitation on use for applications in which PC is contacted with a solvent.
Under such circumstances, for the purpose of improving moldability and chemical resistance of PC, a polymer alloy with a polyester resin such as polyethylene terephthalate resin (hereinafter sometimes referred to as “PET”) and polybutylene terephthalate resin (hereinafter sometimes referred to as “PBT”) has been proposed. However, when PC is mixed with PET or PBT as a modifier, it is difficult to obtain sufficient transparency.
In this regard, a technique of obtaining a transparent composition of PC and a polyester resin in which a transesterification catalyst is blended has been disclosed (for example, Patent Documents 1 and 2). However, there is a problem that foam formation is caused with progression of transesterification.
Further, Patent Document 3 describes that PC and a polyester resin are compatibilized by melting and kneading under a high shear stress. However, when employing such strong kneading, there is a problem that reduction of the molecular weight and heat deterioration of resin are caused by shearing heat.
Patent Document 4 describes that a sheet which is excellent in transparency, mechanical property, thermoformability, etc. can be obtained by finely dispersing PBT in PC and crystallizing the mixture under specific conditions. Meanwhile, Patent Document 5 describes that a resin composition which is excellent in transparency and thermoformability can be obtained by blending a specific polyester resin in PC and PET. However, it cannot be said that transparency in this case is sufficient and further improvement thereof has been desired.
In this regard, Patent Document 6 discloses that a thermoplastic resin composition which is excellent in transparency, heat resistance, chemical resistance and mechanical strength can be obtained by blending PC and a polyester resin containing diol having a cyclic acetal skeleton.
However, when the mixing ratio of PC in the resin composition is high, it is necessary to set a high roll temperature at the time of sheet molding and there is a limitation on equipments. Further, multi-layer sheet molding has a problem that a warpage of a sheet and adhesion to and winding around a roll tend to occur due to the difference of the glass transition temperature from that of other layers.
Moreover, when the mixing ratio of the polyester resin containing diol having a cyclic acetal skeleton is high and the mixing ratio of PC is low, roll contamination and mold contamination tend to occur, and the mechanical strength may be insufficient.
Therefore, a thermoplastic resin composition made of PC and a polyester resin, which is excellent in transparency, mechanical strength and molding processability, and which can be produced stably, and a sheet using the same have been desired.